Could green roofs be the answer to inner-city flooding?


The aim of this experiment was to determine the effect of different materials acting as substrates beneath the top soil and desired plant life. We used a mixture of both organic and inorganic materials to test which substrate proved most effective at retaining water; we believed that the most effective of the substrates would be organic. Before doing this we looked at the effects on a model scaled-down green roof when it was left in the rain constantly over 2 weeks and saw that it retained large amounts of water and in the weeks of warm dry weather following this, the substrate still remained damp to the touch. This could hint at solutions to flooding in cities as Urbanisation is one of the leading causes of flooding in built up areas. This is because there are little to no permeable surfaces for the water to be absorbed by which causes a large amount of water to flow into the storm drains and rivers faster than normal. These storm drains weren’t built to handle the massive amounts of water that can flow into them during a severe storm or heavy downpour which causes street flooding. Having green roofs would provide a permeable surface to absorb the Green roof technology is thought to have been first used in ancient times but these would have been more cave-like in structure. Modern green roof technology however, began in the 1970s in Germany where the first green roof systems had been developed and sold on a large scale to the public, and now a days there are services as Quality roofing and guttering dublin. They\’re among the recommended roofers dublin is proud to boast about. Since then there have been many ventures to make green roof technology cheaper and lighter as a way of restoring nature to large city areas. Roof gardens have also been known to reduce the amount of pollutants in the air by absorbing PM10 emissions as well as Carbon Dioxide, and reducing the amount of storm water that fall from roofs. Prolonging the life membranes (waterproofing) of the roof along with commercial spray foam insulation for the building can create an extra barrier towards heat loss. Due to these factors as well as Green roofs being generally aesthetically pleasing they have become more frequently used. Green roofs are typically built in five layers to replicate the structure of the ground. The first layer normally acts as bedrock to that the roots of any plants growing on the green roof do not grow into the roof of the house and cause damages. The second layer is a protection fleece which adds an extra layer of defence to the waterproofing layer. After this there is a special draining board that is put in place that is especially designed for the green roof. This is bonded with the filter fleece to prevent blockages. Retention cups in the board store water for the plants to grow healthy but will still allow for the drainage of excess water. A layer of the chosen substrate is then put down. This normally consists of brick and organic material, that will allow drainage but also provides a low nutrient medium so the plants do not grow excessively large. The last layer consists of the desired plant life for the green roof; this can vary from grass to wild flowers to sedum. So to test, we created our own model of a green roof in accordance to the specifications to which a green roof is normally built.

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Equipment: Pre-made Green roof model, Tyvek waterproofing, Wood, Nails, Hammer, Coconut matting, Sponge, Carpet Underlay, Grass seeds, Compost, PVA glue, Plastic mesh, measuring cylinder, water, Needle and thread, Stopwatch and a Tray.
Before hand: A green roof model needs to be made in advanced using the wood, Tyvek water proofing, hammer and nails. Also The plastic mesh needs to be sewn together into a bag that is sectioned into three sections long ways and should cover the surface of the green roof. The substrates used for testing which were Coconut matting, Carpet Underlay and sponge should be cut into vertical strips and stuck onto the model above the Tyvek using PVA glue. The plastic mesh bag should be filled with compost and grass seeds and be allowed roughly 3 days to grow.
1. Place the green roof model ontop of the tray which will act as a gutter.
2. Measure 100ml of water using a measuring cylinder.
3. Pour all of the water over one section of the roof making sure that the water is only poured into that section.
4. Allow 60 seconds any water that is not absorbed to collect in the tray.
5. Measure the amount of water that was not absorbed using another measuring cylinder and record results.
6. Repeat for remaining sections of the model
Control Variables: The control variables were the amount of water used, The volume of the substrate and The amount of time the water is left to collect in the tray so that we could ensure a valid comparison of the results. Also the position the model is in the tray, The surface of that the experiment is conducted on are also control variables because if the surface changes the angle at which the model is at could change which would effect the results. Also the same type of grass needs to be used throughout the whole experiment because different types of grass may absorb water at different rates.
Independent Variable: The independent variable is the substrate that is used.
Dependent Variable: The dependent variable is the amount of water that is collected.